The Search Generic field is what you want then. In the settings of Generic Search you need to define which fields you want searched. To the end user all they see is a single search field.
You can see an actual working example on the products page with the Keywords.. In this example, when you enter a key word, it will search through all of the fields such as: title, category, description, etc.
It seems that the "Search Generi Field" is paid, what is a problem for me, since I'm working for another people and they don't intend to spend money. But thanks for your help anyway. Otherwise it is not then possible to perform search vy keyword?